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Building Acoustics

Building acoustics is the science and engineering of achieving a good sound environment within a building space. Building acoustics design is achieved by following an “intelligent layout” where noise producing areas are separated from noise sensitive areas. Acoustics design should also ensure sound insulation between rooms and sound absorption of excess sound to improve communication and reduce noise related distraction.

Sound Insulation and Sound absorption

Sound Insulation (SI):is the reduction of sound (decibel level) as it passes through a partition. A partition can be a wall, ceiling or floor. The passage of sound into one room of a building from a sound source located in another room or outside the building is termed ''sound transmission".

STC or Sound Transmission Class is a single number rating given to panels which indicate the degree of sound transmission loss offered. A higher STC corresponds to a greater degree of sound insulation.

STC / Rw Field STC / Rw Effect/Result
30 22-25 Most sentences are heard and understood clearly.
40 32-35 Speech can be heard with some effort
50 42-45 Loud speech can be heard with some effort. Music is easily heard.
60 52-55 Loud speech is inaudible. Music is heard faintly. Bass is disturbing.
70 62-65 Loud music including bass is heard faintly.
>70 >67 Most sounds are inaudible.

Sound absorption

When sound meets a surface, a part of it is absorbed. The percentage of sound that is absorbed by a material is defined as the ‘Absorption Coefficient’ which is expressed on a scale 0-1. Sound absorption is important because it reduces sound levels inside a room. For good sound insulation, the partition must be capable of blocking airborne sound and the construction must ensure no gaps and leaks using which sound can travel around the partition.

What is Noise Reduction Coefficient (NRC)?

Sound absorption of a material varies with the frequency of sound. NRC is the mathematical average of absorption coefficient of a material at four frequency bands - 250, 500, 1000, 2000 Hz.

Acoustics in open plan offices

Open Plan Office: The benefits and criticisms

The open plan office model has been widely adopted by companies in India and across the world. Although this new model creates an open work environment, it continues to face criticism regarding its acoustic qualities. Some advantages and disadvantages are:

Advantages

  • Encourages team work and transparency
  • Encourages a horizontal hierarchy
  • Cost effective and easier to refurbish

Disadvantages

  • High levels of distraction due to people speaking, phones ringing, etc.
  • Poor environment for higher cognitive tasks such as problem solving and trouble shooting
  • Poor levels of privacy

Subheading/Tab: Why is acoustics important in open plan offices?

  • The open plan office model is the most widely adopted office layout format. Most companies around the world are switching to the open plan model and around 73% of employees work in the open plan office environment (Sykes, 2004).
  • Surveys have shown that poor acoustics is the most frequent complaint by employees citing office noise as a major distraction to their work.
  • Several research studies have proven that office noise severely reduces an employee’s ability to complete cognitively demanding tasks.
  • Along with ventilation and lighting, acoustics is critical to the sense of office comfort.

What does Office Acoustics mean to employees?

  • Higher privacy
  • Better communication
  • Lesser distraction

The three key steps to good office acoustics are:

  • Sound absorption: Reducing excess noise within an office by using sound absorptive materials for internal surfaces and furniture. Reduced noise improves communication between employees and also reduces noise related distraction.
  • Sound insulation: Reducing sound transmission through walls, ceilings, doors and windows is essential for privacy.
  • Zoning: Intelligent layout of an office space keeping acoustics in mind. Often, materials are not the solution but an intelligent layout is.

Why is drywall partitions used in offices?

Drywall partition systems are highly suitable for the modern office space. Some of the advantages of using drywall systems for internal walls are:

  • Ease of installation: Installation time and resources used is significantly lesser than brick and concrete.
  • Lightweight: For large office spaces, the weight of internal walls is a critical design factor. Drywall systems are lightweight and can be installed anywhere in the office, not just on top of the supporting beam.
  • Refurbishment: If a new office layout is implemented, drywall systems can be easily dismantled and set up according to the new configuration.

Why are drywall partitions good sound insulators?

Even though concrete is better at blocking sound than Plasterboard, a drywall system is more effective than a solid concrete wall. How?

The drywall partition works on the mass-spring-mass system. As sound transmits through the partition, the change in medium (from Gypsum to air/Glass Wool to Gypsum) causes high transmission loss. Therefore, the sound transmitted onto the other side is much weaker.

Why are drywall partitions better insulators than brick or concrete?

  • Sound insulation decreases with stiffness: The more rigid the material the worse its sound insulation. Therefore, brick and concrete are not preferred sound insulators.
  • Impractical for large construction projects: Though, heavier mass implies greater sound insulation, for every additional 6 dB of insulation, mass has to be doubled which is very impractical for large construction projects. Brick and concrete are weak absorbers: Brick and concrete are highly reflective. Although they may prevent sound from transmitting through the wall, they do not absorb the sound but simply reflect it back into the room.
  • This runs the high risk of creating a noisy internal environment.

Importance of false ceilings in acoustics:

  • The roof of an indoor space provides the largest available cross sectional area for sound absorption material and reducing overall sound level.
  • False ceilings contain an air cavity behind which provides good sound insulation from the floors above.

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